1. Field of the Invention
This invention relates generally to integrated circuits, and more particularly to techniques used to determine the internal workings of an integrated circuit through analysis electro-magnetic emissions.
2. Description of the Background Art
Integrated circuits (IC) are miniaturized electronic circuits consisting mainly of semiconductors and passive devices. Due to their relatively small size, high performance, and low cost, ICs have become quite common in almost every electronic device manufactured today. In most instances, ICs range in size from only a few square millimeters up to around 250 square millimeters. While this small size is great for packaging within electronic devices, it often makes troubleshooting and quality control very difficult.
The testing of ICs is typically done at least twice during the manufacturing process; once at the wafer stage, and once as the individual ICs are packaged in an electronic device. Automated test equipment (ATE) such as wafer probes are the most common means for testing ICs. A wafer prober uses a probe card as an interface between the electronic test equipment and an IC. The problem with wafer probing is that it requires highly sophisticated and expensive test equipment, and it is very time consuming. Additionally, the equipment must also be calibrated such that it does not damage the IC during testing.
In order to reduce the time and costs associated with IC testing, ICs are often designed with testability features. The problem with testing only the testability features is that it is often difficult to determine if the IC is indeed operating properly by only testing a select few features. This type of testing more typically filters functional devices from non-functional devices.
One of the largest obstacles in IC testing is the testing of clock signals. Integrated circuits often include one or more clock signals for coordinating the actions of two or more circuits. These clock signals oscillate between a high and low state at a predetermined clock rate (cycles per second, as measured in Hertz). The clock signal(s) are used to synchronize different parts of the circuit, and also to account for delays in transmission. As ICs become more complex, a particular IC may have many clock signals present, with various different clock rates. It is often difficult to determine if the clock rates are operating properly via known test procedures.
As may be appreciated, if a clock signal is operational, but is either inaccurate or not properly synchronized, certain functions or calculations may not be performed correctly by the IC, resulting in a functional, yet defective device. Such devices are often difficult to diagnose or identify through known test procedures.
Additionally, often times manufacturers may find it necessary to reverse engineer products. Whether it be their own ICs, competitor's ICs, or vendor's ICs, reverse engineering is a useful tool in designing, diagnosing, and improving IC's. This practice up until now has included much of the previously described IC testing procedures, as well as some dissection type procedures. The problem has been that in addition to the expensive test equipment required, the process is typically destructive, and may require multiple trained professionals to decipher functions from parts. Indeed, this destructive type reverse engineering may be particularly troublesome if there is only one sample to work with.
What is needed, therefore, is a non-destructive system and method for testing the operation of internal clocks of integrated circuits.